The Common Public Radio Interface (CPRI) specification is published together by several companies which co-operate in the CPRI industry for the key internal interface in a radio base station for mobile communications. This CPRI specification is the first common specification in connection with the key interface, and provides a set of common standards for the key internal interface in the base station. The CPRI is responsible for defining the key internal interface in the radio base station between a Radio Equipment Controller (REC) and a Radio Equipment (RE). Here, the REC includes a baseband processing element and the RE includes a Radio Frequency (RF) processing element. This standard has been established for the purpose of creating an open market orientated to cellular base stations, and thereby greatly reducing enormous development labors and high costs conventionally concomitant throughout the design of a base station.
The CPRI industry cooperation focuses on a design for a base station of a 3rd Generation (3G) mobile communication system, and this design divides the radio base station into a radio part and a control part by specifying such a new interface which is the interconnection point internal to the base station only and uniquely driven by radio. This allows each part of the base station better benefit from the technology evolution in its respective area. The CPRI specification is openly available for the benefit of the wireless industry. Key benefits for network operators are the availability of a wider portfolio of radio base station products and the adaptability to all deployment scenarios with a shorter time to market. In addition to this, the CPRI specification enables base station manufacturers and component providers to focus their research and development efforts on their core competencies. The CPRI specification allows for new architectures and is not limited by module dimensions or a predefined function split.
In addition to focus the base station manufactures' research and development efforts on their core competencies, the CPRI industry cooperation also gives rise to equipments manufactured by different vendors. The CPRI specification brings the primary benefits in that it allows newly introduced technologies to evolve more rapidly, and enables the base station manufacturers to provide the operators a wider portfolio of products and to introduce their products into the market in a shorter period. Meanwhile, the operators may benefit from wider product options, more flexible solutions and an improved efficiency of network deployments.
The founders of the CPRI initiate a competitive mobile network component industry, and benefit the entire wireless industry by making the CPRI available openly. The CPRI is a complementary to existing standardization organizations, such as the 3rd Generation Partnership Project (3GPP), and its developed common interface may be applied to radio base station products of mobile systems.
For a 3G mobile communication system, such as a Wideband Code Division Multiple Access (WCDMA) system, the CPRI specification may be adapted to implement Layer 1 (L1) and Layer 2 (L2) communication protocols between a baseband control element and an RF element. Based on the CPRI specification, the commonality of the interface between the baseband control element and the RF element may be enhanced, and it is also advantageous for the interconnection between the baseband unit and the radio frequency unit from various vendors. Subsequent to the successful introduction of the CPRI, an issue in urgent need of being addressed at present is how to update and enhance the systematic architecture and the networking mode of 3G radio base stations. For a common interface between the baseband unit and the RF unit, both a systematic architecture and a networking mode need to be proposed accordingly for making full use of its advantages. In addition, a solution to network transport reliability needs to be provided based on the systematic architecture. It is also required to ensure the integrity, compatibility and reliability of a base station system in the case of the common interface architecture and the coordination between apparatuses from different vendors.
It may be seen from the evolutions of the 2nd Global System of Mobile Communication (GSM) and the WCDMA that a base station experiences a great renovation every four to five years. Furthermore, thanks to rapid developments of computing and microelectronic technologies, the regeneration of mobile communication technologies will be increasingly rapid. During the evolution of various phases, various radio standards emerge constantly and will exist concurrently, such as the 2nd GSM, the 3rd WCDMA, the CDMA2000, the Time Division-Synchronous Code Division Multiple Access (TS-CDMA), the Worldwide Interoperability Microwave Access (WiMAX) of the 802.16d and 802.16e from the Institute of Electrical and Electronic Engineers (IEEE), etc. As a common radio interface in the industry the CPRI must be adapted to a common transmission for various standards, thus embodying the connotation of the so-called common interface.
The organizations of radio frame timing and radio frame number as well as data rate are different for different radio standards in different phases. The radio frame timing identifies a signal that indicates the start of a period for a radio frame from a radio base station. Different radio standards are usually provided with different frame periods, for example, a frame period of 10 ms (millisecond) for the WCDMA R6 and the earlier versions, a frame period of 60/13 ms for the GSM, and numerous options, including 2 ms, 5 ms and the like, of a frame period for the 802.16e, etc. The radio frame number refers to a serial number of a radio frame. Different standards are provided with different methods for identifying the radio frame number and with different numbers of binary bits, for instance, a 12-bit radio frame number for the WCDMA R6 and earlier versions, and a more complex one for the GSM.
The radio data generally refer to a data flow of two components, i.e. In-phase/Quadrature (IQ), after a modulation. Thus, the user plane data from the REC to the RE and that from the RE to the REC may be transferred in the form of IQ data. Typically, IQ data are transported in an IQ container, also known as an Antenna xCarrier (AxC) container in the CPRI (see the CPRI specification for more details), which will be directly referred to as an IQ container for convenient understanding.
For the radio IQ data of specific standards, an IQ container mapping shall be enabled in view of different data rates for the standards. A primary one of the factors, which has influence upon the complexity for mapping the IQ data into a CPRI IQ container in different standards, is the standard rate of various standards. For the CDMA scheme, the standard rate refers to a chip rate (3.84 MHz for the WCDMA, 1.2288 MHz for the CDMA 2000 and 1.28 MHz for the TD-SCDMA); for the GSM, the standard rate refers to a symbol rate of 13/48 MHz; and for the WiMAX, the standard rate refers to a sampling frequency, for which there are numerous options available, as illustrated in Table 1. Note that the standard rate is not a naming common to the industry, but as used here is an assumed concept in general for a description of various standards. Moreover, a standard period is defined as an inversion of the standard rate, which refers to a chip period for the CDMA, a symbol period for the GSM, and a sampling period for the WiMAX.
TABLE 1Overview of 16d/e Baseband FrequenciesChannelNumber ofBandwidth (MHz)Sampling Rate (MHz)Multiplexing (n)1.75/3.5/7/14/282.0/4.0/8.0/16.0/32.08/71.5/3/6/12/241.72/3.44/6.88/13.76/27.5286/751.25/2.5/5/10/201.44/2.88/5.76/11.52/23.04144/1252.75/5.5/11/223.16/6.32/12.64/25.28316/2752.0/4/8/16/322.28/4.56/9.12/18.24/36/4857/50Others/8/7
As a common interface standard used between the REC and RE, the CPRI serves to provide a method for transferring various standards of radio IQ data. The latest version of the CPRI, i.e., V2.0, is designed for the WCDMA R6 and the earlier standards, and hence is neither suitable for other standards such as the IEEE 802.16e, the GSM, etc., nor possibly even for subsequent WCDMA versions such as the WCDMA R7, etc. To adapt to the technology advancements in the mobile communication industry, a common radio interface is urgently needed for convenient and efficient transfer of multi-standard radio service data.